Breathable waterproof fabric

ABSTRACT

A breathable-waterproof material is given wherein an extensively fibrillated thermoplastic resin material is formed which permits high water vapor transmission levels while substantially precluding liquid water penetration.

Unit ed Sttes Patent Gallacher [4 1 July 11, 1972 [54] BREATHABLEWATERPROOF FABRIC [56] References Cited [72] Inventor: Lawrence VincentGallacher, Norwalk, UNITED STATES PATENTS Conn. 2,933,154 4/1960Lauterbach ..55/528 X 1 Asslgneev American Cyanamid p y Stamford,3,197,946 8/1965 Taylor Conn- 3,262,834 7/1966 Abell et a] 4 Masanon X[21] Appl.N0 121,094 PrimuryExaminer-Reu-ben Friedman AssistantExaminer-R. W. Burks Related US. Application Data Anomey james Laughlin,JL [63] Continuation-impart of Ser. No. 820,761, May 1,

1969, abandoned. [57] ABSTRACT A breathable-waterproof material is givenwherein an exten- [52] U.S. Cl ..55/l6, 55/524 sively fibrillatedthermoplastic resin material is formed which 51 1111. C1. ..B0ld 39/16,BOld 49/00; pen-nits high water vapor transmission lgvels while submn,[58] Field of Search 161/159, DIG. 2; 55/ l 6, 36, tiauy precludingliquid water penetration 7Clains, 6Drawiring Figures PKTENTEDJUL 1 1 m23,675,391

/ susznora INVENTOR LAWRENCE V. GALLAGHER jnf- PATENTEBJHL H mm3.675.391

sum 2 or a INVENTOR LAWRENCE V. GALLAGHER B YJ ll. m l-Ah.

' ATTORNEY 16mm 1 m2 WEN SHiET 3 OF 3 FIGS INVENTOR GALLAGHER may.

LAWRENCE V.

ATTORNEY BREATHABLE WATERPROOF FABRIC This application is acontinuation-in-part of my prior application, Ser. No. 820,761, filedMay 1, 1969, now abandoned.

This invention relates to a new composite material. More particularlythis invention relates to novel breathable-waterproof material orcomposite which permits high water vapor transmission while retardingliquid water penetration. In particular this invention relates to amethod of protecting an environment from water in the liquid phase whilepermitting the transmission of water in the vapor phase. In oneembodiment this invention relates to material which is useful asrainwear.

Conventional fabrics without surface treatments function poorly inapplications where water repellency is required. The major reasons forthis deficiency are well known: improper surface characteristicspennitting wetting, and open construction which facilitates the passageof water through the material. It is a simple matter to correct this byadding a continuous barrier layer to the fabric, as in the case ofrubber or vinylcoated fabrics, and such materials are essentiallyperfect barriers to liquid water. However, the same materials arebarriers to liquid water. However, the same materials are barriers aswell to the passage of air and water vapor, and this seriously detractsfrom the comfort of rainwear based on the fabric. Thus, ideally,rainwear material should be a water barrier and yet be breathable, thatis, highly permeable to water-vapor or air.

One approach to the problem is to employ tightly woven fabrics whichhave been treated with surface finishes to render them non-wettable.Such treatments have not been completely successful because thesesurface finishes are not permanent and are ineffective against water atsignificant pressures, such as, for example, in driving rain or sittingon wet clothing. Another approach to the problem has been to coat thefabric with a thin microporous coating. This approach is limitedinherently in not being able to impart effective water rejection andbreathability simultaneously.

It is an object of this invention to provide a thermoplastic materialwhich is unique in that it functions as a barrier to liquid water whileat the same time permitting high air and water vapor transmission.

This and other objects are accomplished by the use of a novelthermoplastic resin which has been processed to a unique fibrillar form.My solution to the problem of combining water rejection andbreathability is based on utilizing this unique type of fibrillar formstructure or material.

This unique material employed in this invention is formed by theaddition of a primary solid particulate thermoplastic resin which ischaracterized by being insoluble in a selected leaching agent or solventto a secondary thermoplastic resin which serves as a dispersing matrixand is characterized by being soluble in the selected leaching agent orsolvent. It has been surprisingly found that if these resins are mixedand sub jected to shearing action at temperatures above or just slightlybelow the melting point of the primary resin, a continuous fibrillatedmat or web-type structure is formed by the primary resin. Thisfibrillated structure of the primary resin in the secondary resin matrixcan then be leached with the selective solvent which removes thesecondary resin leaving behind the extensively fibrillated structure. Ifthe material is compressed before leaching, the nature of thefibrillation changes within the structure resulting in enhancement ofthe permeability.

This material, the extensively fibrillated sheet structure used in thisinvention may be more precisely characterized as having the form of acontinuous or nearly continuous and integral three dimensional networkor structure containing interconnected branching ribbons and ligaments,with the principal surfaces of the ribbons arranged parallel to theplane of the sheet. The thickness of the ribbon-like elements rangesfrom about 0.3 to microns and preferably in the range of l to 9 microns.The widths are not as well defined because of extensive lateralbranching, but generally they are in the range of about 0.3 to 40microns and preferably they are from about 2 to microns. In many casesthe ribbons and ligaments conribbons tinue nearly the whole length ofthe sheet. Generally they are at least 1 inch in length and preferablyat least 200 microns. Within the fibrillar structure itself are voidareas between the which are substantially uniformly dispersed throughoutthe material with major dimensions essentially parallel to the sheet.The density of the sheet ranges from about 0.25 to about 0.6 andpreferably from about 0.3 to about 0.5. Average void thickness which isthe smallest dimension of the void, is approximately 1 micron with arange from 0 to 25 microns. This structure is essentially the same forall fiber-forming semi-crystalline thermoplastic polymers such aspolyolefins, polyesters, polyamides and others when fibrillatedaccording to this invention.

FIGS. 1 through 6 show fibrillated structures at various magnificationsand are representative of the types of structure found in thisinvention. Identically similar structures are achieved when two or moresemi-crystalline thermoplastic polymers are fibrillated.

More specifically, a fiber-forming semi-crystalline thermoplastic resinsuch as, for example, polyethylene, polypropylene, poly( l-butene), poly(4-methy1pentene), poly (glycolic acid), poly (ethylene terephthalate),poly(hexamethylene sebacamide), other polyolefins, polyesters, orpolyamides, copolymers containing these polymers or mixtures of these orother semi-crystalline thermoplastic polymers is dispersed in a resinmatrix such as, for example, poly(methyl methacrylate), polystyrene,polyisobutylene, poly(vinyl acetate), poly(ethylene oxide) and others,either plasticized or unplasticized, singly or in combination, at atemperature above the melting point of the thermoplastic resin. Thesecondary resin is conveniently selected on the basis of its solubilityin a selected solvent as opposed to the insolubility of the fiberformingsemi-crystalline thermoplastic resin in the same select solvent and theworkable temperature of the secondary resin. It is important that thesecondary resin be workable at the temperature selected and comparablein melt viscosity to the fiber-forming component at the workingtemperature. Thus, for example, if polyethylene is selected as thefiber-forming semi-crystalline thermoplastic resin and poly(methylmethacrylate) is selected as the secondary resin forming the resinmatrix, the working temperature of the dispersion should be from aboutto about 250 C. and preferably from about to about C.

Further, the chemical natures of the matrix and fibrillator areimportant, for the interactions of the two phases at their interfacedepend upon them. It is for this reason, it is believed, thatpolystyrene and poly(methyl methacrylate) matrices impart differentproperties to poly-(l-butene), and polyolefin fibrillar materials areimproved when the poly(methyl methacrylate) matrix is modified withpoly(ethylene oxide). Surface forces tend to relax the ribbon-likestructural elements toward rod-like, round cross-sections in oppositionto viscous forces and, therefore, it is desirable to keep viscositieshigh and surface energy low. Modification of poly(methyl methacrylate)with poly(ethylene oxide) appears to produce low surface energies withpolyolefins and a number of other polymers.

Dispersion, mixing, and blending are important and may be accomplishedon a twin-screw extruder, two-roll mill or other conventional high shearmixing device. Once the resin blend is uniform and the mixing welladvanced, continued shear will cause orientation and fibrillation of thethermoplastic resin. At this point the temperature may be maintained atthe original level or may be lowered to increase the orientation andfibrillation. Ordinarily some of this fibrillation takes place in thecompounding or mixing operation. After mixing, the resin-matrix mixturemay be compressed, extruded, or treated in any other conventional way toachieve shear within the matrix thus causing or enhancing theorientation and fibrillation of the thermoplastic resin.

Subsequently, the prepared resin matrix mixture is treated with anappropriate leaching solvent such as, for example, toluene, acetone,ethylene dichloride, methylene chloride,

methyl alcohol, or other appropriately selected solvents which extract,leach, or dissolve the secondary resin or resin matrix thus leaving thefibrillated product. This extraction may be carried out by anyconventional manner such as soaking or spraying and may be acceleratedby heat, providing, however, that care be taken to maintain thefibrillated structure.

Our solution to this problem of combining water rejection andbreathability is based upon utilizing this unique type of structure.Typically, a blend of 9 parts by weight polyolefin, and optionally 1part by weight polytetrafluoroethylene, and 27 parts by weight ofmodified poly(methyl methacrylate) matrix is compounded above themelting point of the polyolefin and softening point of the modifiedpoly(methyl methacrylate), and then extruded to form a sheet. This istreated with methylene chloride to extract the soluble matrix, leavingbehind a soft sheet of fibrillated polyolefin andpolytetrafluoroethylene if added.

Microscopic examination of the sheet reveals a network of micro-ribbons,ligaments, and fibrils. For example, H6. 3 is a micrograph of a typicalcross-section of a polypropylene sheet which has been sectioned parallelto the flow direction. Here we are looking at the leading edges of theribbons. hi this case which is typical, the width of the ribbons rangesfrom about 0.3 to 40 microns. However, it can be easily ascertained thatthe typical ribbons have a width of about 20 microns. In like manner theribbon thickness ranges from about 0.3 to 20 microns, but it can beeasily seen that they typically are about 8 microns. The vertical spacebetween the ribbons averages about 1 to 2 microns and ranges from nearlyto 20 microns.

While different materials and process variations may vary these valuesfor ribbon width, thickness, pore size, etc., these are typical andrepresentative generally of the structures found in this invention.Within the scope of this invention are ribbon, fibril, or ligamentstructures which have a width to thickness ratio from 1:1 to llzlalthough i prefer ranges of from about 3:1 to 8:1.

FIG. 2 is a top view of the polypropylene structure and it shows thatthe lengths of the ribbons are typically greater than the microscopicdimensions. In fact they are usually larger than 1 inch although thiscan vary greatly depending upon the material system and process.Preferably the length of these structures is at least 200 microns. Thenetwork is aligned principally in the flow direction. However, there aremany internal connections between fibrils and ribbons so that theextracted sheet is quite coherent and strong.

FIGS. 5 and 6 are 1,000X and 3,000 magnifications of a poly( l-butene)system containing 10 percent polytetrafluoroethylene. FIG. 5 is a sideedge view at 1,000X magnification. At this level most of the apparentstructural features consist of polyolefin micro-ribbons and filaments.FIG. 6 at the higher magnification reveals the polytetrafluoroethylenestructure which has the form of a three-dimensional network of very finefibrils. This polytetrafluoroethylene sub-structure consists of fibrilswhich generally connect and penetrate the polyolefin ribbons. There is agreat deal of entanglement, and the fibrils range from less than 0.02microns to 0.2 microns in diameter with inter fiber spacings rangingfrom about 0 to 3 microns. The polytetrafluoroethylene sub-structurecontributes much to the overall physical strength of the sheet.

FIG. I is a 300 magnification of low density polyethylene while FIG. 4is a l,000 magnification of poly (glycolic acid). The consistency of thegeneral structures of this invention are easily seen.

The structure described here is not only ideally suited for the task ofrejecting liquid water, but for permitting the passage of water vaporand air. Movement of gases through solid media generally occurs via theclassical permeation route of solution/diffusion or by gaseous diffusionthrough continuous pores or openings. The latter mechanism is muchfaster for transport of gases through all but sub-micron films, and isthe mechanism of choice here. Thus it has been found that thefibrillated sheets of this invention have very high water-vaportransmissions, with values comparable to conventional woven fabrics. Airalso passes quickly through the material at low pressure. It is evidentthat gases pass through this material by following continuous openpaths. This same structure appears to block the passage of liquid water.

While I do not wish to be bound by any theoretical explanation I believethis invention is made possible by a combination of size and surfaceforce effects. The wetting of solid surfaces by liquids is a function ofthe surface tension of each phase ('y and-y and the interfacial tension(37;). These parameters determine the contact angle 9, which is theangle formed by a drop of the liquid on the surface. The relationshipbetween 0 and the surface tensions is given by the Young equation:

If B is less than the liquid tends to advance on the surface to achievean equilibrium value of 6, while if 0 exceeds 90, the liquid tends notto spread. When 6 reaches no wetting occurs. If 0 is greater than 90 andthe solid is porous, a critical pressure on the liquid must be exceededbefore it will penetrate the pores. This pressure is given by theWashburn equation,

where P is the pressure, 'y the surface tension of the liquid, and r theradius of the pore being penetrated. It is believed this expression canbe applied to the unique fibrillated structures described herein with 2rtaken as the smallest dimension of the free-space or voids between theribbons. If the pressure does not reach the critical value as defined bythe equation given above, penetration will not occur. Taking this as anequilibrium effect, the thickness of the fibrillated structure or sheetshould not matter and the only important consideration is the smallestgap the liquid must pass through in each continuous path through thesheet. Of course, in any situation where there are only a few gapsinvolved per path, the probability of encountering a small limiting gapwill increase with thickness. Further, since the paths are necessarilyquite long compared to the thickness of the sheet because of the ribbondimensions, there will be appreciable kinetic effects retarding movementof the liquid through the sheet even when the critical pressure isexceeded. Finally, the application of force normal to the surface of thematerial will compress it and thereby tend to decrease the widths of theinternal spacings, which are generally aligned parallel to the surfaces.

For liquid water repellency, a material which forms contact angles of 90or greater with water is needed. Polyolefins including polyethylene,poly( l-butene) and others, and polytetrafluoroethylene are suchmaterials. Further, there is a hysteresis effect which leads to contactangles for advancing liquid fronts larger than those for recedingliquids. Approximate advancing contact angles with water and openingspenetrated atone atmosphere of pressure are given below.

Water/Polymer Advancing Contact Angle Minimum Opening Penetrated at 1atmosphere, Polyethylene 99 .45 microns Polypropylene [06 .80 micronsPolytetrafluoroethylene 1 12 1.08 microns It can be seen from the tablethat polyethylene/polytetrafluoroethylene combinations should performvery well as liquid water barriers, as indeed they do. Further, one candeduce that for service at lower hydrostatic pressures, polyolefinsshould function adequately without polytetrafluoroethylene. Similarly,polytetrafluoroethylene can be used by itself in certain instances, orcan be used in conjunction with other polymers with smaller contactangles to up-grade their water repellent characteristics. These includepolyesters, polyamides, and mixtures of the same.

Thus it is easily seen that this novel fibrillated material may be usedto protect environments from any type of liquid penetration when theliquid forms a contact angle with the material of about 90 or greater.At the same time gas transmission in either direction will in many casesnot be effected.

While we have discussed some specific materials, any high molecularweight, fiber forming semi-crystalline thermoplastic polymer iseffective in the invention. The unique product of this invention isparticularly effective in protecting against liquid water penetration.Thus this material is very satisfactory for rain and other foul weatherwear. When used, for example, as rainwear, it protects the user fromliquid water and at the same time the natural moisture of the user isallowed to escape thus increasing the wearers personal comfort. Becausethe unique material employed is soft and flexible, it is particularlyuseful in clothing applications such as, for example, coats, gloves andthe like. It may likewise be used in outdoor tenting and otherapplications where it is desired to have vapor transmission in eitherdirection while at the same time precluding liquid water penetration.The material may be used in gasliquid membrane systems and in anyvariety of other ways where it is desired to protect any environmentfrom liquid penetration while permitting gas to freely pass.

The following examples embody particular modes of this invention but arenot intended to limit the invention except as appears appended from theclaims. All pans are by weight unless otherwise stated.

EXAMPLE 1 Sixty parts by weight of molding grade poly(methylmethacrylate) pellets, parts of powdered high molecular weightpoly(ethylene oxide), 27 parts of isotactic poly( l-butene) pellets, and3 parts of poly-(tetrafluoroethylene) in aqueous dispersion form werecombined in a ribbon blender at room temperature. The resulting mixturewas charged to a twin-screw extruder and melt compounded at about 200 C.The product was extruded to form a continuous sheet 10 mils thick. Thesheet was cut into 12 inch squares which were then immersed in methylenechloride at room temperature to extract substantially all (99 percent+)of the poly(methyl methacrylate) and poly(ethylene oxide) within 3hours. The resulting product was a sheet structure of microporousfibrillar poly (l-butene) and poly(tetrafluoroethylene) and was quitesoft and esthetically pleasing.

These sheets were tested by the Hydrostatic Pressure Method according toFederal Test Method Standard No. 191, Method 5512 (Dec. 31 1968) todetermine the resistance of the material to the passage of water underpressure. Essen tially the specimen was placed between two annular planeclamping surfaces and hydraulic pressure was applied to the underside ofthe clamped surface by means of a piston. At the first appearance ofwater through the specimen, the pressure was recorded.

Water vapor transmission was determined by the standard ASTME-96,Procedure B.

The results of these tests are shown below.

Water Resistance 16 psi Water Vapor Transmission Example 1 l 100gms/m-24 hours EXAMPLE 2 EXAMPLE 3 The liquid water penetration underpressure was determined for a number of materials and materialscomposites including the materials of this invention. The test wasconducted by employing glass syringes having bore areas of 0.31 squareinches or 0.44 square inches. Each syringe was filled with water andplaced with the base flat on top of the material to be tested andunderneath was a piece of blotting paper. Various weights were placed onthe plunger of the syringe in order to establish a force per unit areaand observations were made as to whether the water penetrated the fabricand it was determined whether the paper was wetted or not.

The following materials were tested:

A. Commercial water repellent polyester/cotton rainwear fabric B Wovenpolyester cotton fabric with a microporous coating of polyurethane(Reevair) C. Supported Vinyl fabric (Naugahyde) D Fibrillatedpolyethylene E Fibrillated polyethylene with 10 percentpolytetrafluoroethylene F. Fibrillated poly( l-butene)polytetrafluoroethylene The same water vapor transmission test employedin Exampie 1 was employed. In addition, air transmission measurementswere made using Federal Test Method Standard No. 191, Method 5452. Theresults of these tests were recorded in Table l.

with 10 percent 1. A method of protecting an environment from water inthe liquid phase while permitting the transmission of gases selectedfrom the group consisting of water vapor and air comprising interposingbetween the environment to be protected and the source of water in theliquid phase a semi-crystalline thermoplastic high molecular weightpolymer having a web structure of the form of a continuous and integralthreedimensional network of interconnected ribbons and ligaments, saidribbons and ligaments being oriented uniaxially and having widthsranging from about 0.3 to about 40 microns, thicknesses ranging fromabout 0.3 to about 20 microns, lengths of at least 200 microns, andhaving void areas substantially uniformly dispersed throughout thematerial with major dimensions essentially parallel to the plane of thesheet, said voids being ribbon-like in form and having apparentthickness of less than about 25 microns.

2. The method according to claim 1 wherein the polymer is a fiberforming polyolefin.

3. The method according to claim 2 wherein the polymer is selected froma group consisting of polyethylene, isotactic polypropylene, isotacticpoly( l-butene), and isotactic poly (4- methyl pentene).

4. The method according to. claim 1 wherein the semicrystallinethermoplastic high molecular weight polymer is selected from the groupconsisting of polyolefins, polyesters, polyamides, and mixtures of thesame, and is admixed with polytetrafluoroethylene.

5. The method according to claim 4 wherein the polymer is selected fromthe group consisting of polyethylene, isotactic polypropylene, isotacticpoly(1-butene), isotactic poly (4- methyl pentene), poly(glycolic acid),Job ethylene terephthalate), the polyamide of 12 IZ-aminododecanoicacid, and poly(hexamethylene sebac amide) and mixtures of the same.

6. The method according to claim 1 wherein the semicrystallinethermoplastic high molecular weight polymer comprises a network ofribbons and ligaments wherein the ribbon \lvidth to thickness is in aratio from about 1 to l to about 1 l to 7. The method according to claim1 wherein the ribbon 5 to thickness is in a ratio of from about 3 to lto about 8

2. The method according to claim 1 wherein the polymer is a fiberforming polyolefin.
 3. The method according to claim 2 wherein thepolymer is selected from a group consisting of polyethylene, isotacticpolypropylene, isotactic poly(1-butene), and isotactic poly (4-methylpentene).
 4. The method according to claim 1 wherein thesemi-crystalline thermoplastic high molecular weight polymer is selectedfrom the group consisting of polyolefins, polyesters, polyamides, andmixtures of the same, and is admixed with polytetrafluoroethylene. 5.The method according to claim 4 wherein the polymer is selected from thegroup consisting of polyethylene, isotactic polypropylene, isotacticpoly(1-butene), isotactic poly (4-methyl pentene), poly(glycolic acid),poly(ethylene terephthalate), the polyamide of 12 -aminododecanoic acid,and poly(hexamethylene sebac amide) and mixtures of the same.
 6. Themethod according to claim 1 wherein the semi-crystalline thermoplastichigh molecular weight polymer comprises a network of ribbons andligaments wherein the ribbon width to thickness is in a ratio from about1 to 1 to about 11 to
 1. 7. The method according to claim 1 wherein theribbon width to thickness is in a ratio of from about 3 to 1 to about 8to 1.